Glossary · Control theory and process control
PID controller
Also known as: Proportional-integral-derivative controller, Three-term controller
German: PID-Regler
In control engineering, a PID controller computes its output from three terms of the control error: a proportional term for the current error, an integral term for the accumulated error and a derivative term for its rate of change.
- Control theory
In one sentence
A PID controller computes its output from proportional, integral and derivative terms of the control error; it is the standard loop controller.
Example
In the PLC, a PID function block controls the temperature of a heating zone: it reads the thermocouple value, compares it with the setpoint and writes the heater output every 100 ms.
How it applies
- Engineering: PID controllers run as function blocks in a Programmable logic controller (PLC), a DCS or a compact controller. Implementations differ in structure (ideal, parallel, series), in whether P and D act on error or measurement and in parameter units, so parameters cannot be copied between vendors without conversion.
- Operation: Operators work with the controller through a Faceplate: mode, setpoint, output and alarms.
- Maintenance: Many loops in the field run poorly tuned or in manual. Loop performance reviews and Controller tuning are ongoing tasks.
- Documentation: For each loop, document structure, active terms, parameters with units, output limits, Anti-windup and Bumpless transfer behavior. Map vendor parameter names in the terminology database.
PID controller vs. PID algorithm
The PID algorithm is the mathematical law. A PID controller in practice also includes modes, limits, filters, alarms and tracking; most field problems arise in these parts, not in the three terms.